Device for maintaining constant the tension of a web pulled through printing units of a printing press

ABSTRACT

A device for maintaining constant the tension of a paper web withdrawn from a supply roll and conveyed through one or more printing units of a printing press by two couples of power-driven rollers disposed anterior and posterior, respectively, of the unit or units includes measuring means for measuring and visually preferably digitally indicating speed differentials between the two couples and speed regulating means for setting the relative speed of the couples for a selected value. These regulating means are complemented and act in conjunction with control means which automatically maintain the tension of the web portion between the anterior couple and the next adjacent printing unit at a selected constant value.

United States Patent DEVICE FOR MAINTAINING CONSTANT THE TENSION OF AWEB PULLED THROUGH PRINTING UNITS OF A PRINTING PRESS 5 Claims, 1Drawing Fig.

U.S. Cl 226/25, 226/40,226/30,226/111 Int. Cl B65h 25/22 Field of Search226/25, 40,

Primary ExaminerAllen N. Knowles Att0rneyHane and Baxley ABSTRACT: Adevice for maintaining constant the tension of a paper web withdrawnfrom a supply roll and conveyed through one or more printing units of aprinting press by two couples of power-driven rollers disposed anteriorand posterior, respectively, of the unit or units includes measuringmeans for measuring and visually preferably digitally indicating speeddifferentials between the two couples and speed regulating means forsetting the relative speed of the couples for a selected value. Theseregulating means are complemented and act in conjunction with controlmeans which automatically maintain the tension of the web portionbetween the anterior couple and the next adjacent printing unit at aselected constant value.

I PATENTED FEB 915m Inventor: Hnmw Gnzrmen DEVXCE FOR MAINTAININGCONSTANT THE TENSEON OF A WEB PULLED THROUGH PRINTTNG UNITS OE APRINTING PRESS The invention relates to a device for maintainingconstant the tension of a web such as a paper web guided through aprinting press, and more particularly, to a device for maintainingconstant the tension of a web which is pulled through one or moreprinting units of the press by couples of conveyor rollers disposedanterior and posterior, respectively, of the printing units andpower-driven at finely variable speeds.

BACKGROUND It is known for web-fed rotary presses to withdraw the web,such as a paper web upon which printing is to be effected from a supplyroll and to convey the web through one or more print ing units of thepress and subsequently through one or more drying and cooling units. Theindividual printing inks are applied to the web in succession and suchapplication must be accurately registered. To obtain such accurateregistration of the inks, it is necessary that the web is maintained atconstant tension while traveling along the length of the press. As isevident, changes in the tension of the web affect directly the physicalshape of the web by variations of the stretch experienced by the web dueto changes in its tension-such changes in shape due to variations in thestretch are particularly pronounced with offset printing pressesoperating with dampeners. Moreover, changes in tension affect theconditions under which the printing operation proper is carried out suchas the slip of the web between the impression cylinders. As a result, acorrectly registered multiple color printing becomes impossible, or atleast very difficult.

The aforepointed out technical problem is well understood in the art andmany proposals have been made to overcome the same.

According to French Pat. No. 426,833 the tension of the web is regulatedby changes in the rotational speed of a couple of rollers withdrawingthe web from a supply roll. Such changes in speed are controlled by thedeflection of a pendulum roll engaging the web with constant pressure.Such very simple and primitive web tension control is capable only ofeliminating disturbances as are caused by and during the withdrawal ofthe web from the supply roll.

Published German Pat. Application No. 1,060,406 discloses a printingpress in which couples of power-driven conveyor rollers are disposedanterior and posterior of the printing unit or units of the press. Therotational speeds of the couples are manually adjustable independentlyof each other. The application also refers to mean for measuring andcontrolling the web tension, but does not further describe such means.

A device of this kind subdivides in effect the web into several alignedand mutually separate web portions along the length of the members andthese portions are adjustable independently of each other. As a result,there is no assurance that the tension of the web is stable and constantacross the entire length of the web part passing through the press.Moreover, if a web is to be printed upon on both sides it is notpossible to provide tension probing devices at arbitrary points of theweb as a smearing of the freshly printed ink must obviously be avoided.

US. Pat. No. 2,897,754 discloses a device in which the withdrawal speedof the web is controlled by a friction belt drive acting upon thecircumference of the web supply roll. The driving speed of the beltdrive is controlled by the interposition of a finely adjustable speedvariable gearing, which in turn is controlled by the displacement of atension roller disposed posterior of the supply roll and acting upon theweb as the same is withdrawn from the roll. The device according to thepatent also provides that the rotational speed of the couples ofconveyor rollers disposed posterior of the printing units of the pressand anterior of drying units is variable by suitably connected finelyadjustable variable speed gearings. The patent is silent as to theconditions which are to be taken 0 unit of time is digitally indicated.The pulse counts are used for measurements of slippage and ratios ofrotation. The relative rotational speeds of the conveyor rollers and thecooling rollers are then adjusted, either by automatic or manualcontrol.

However, maintaining a definite speed ratio between the conveyor rollersand the cooling rollers is not at all sufficient to obtain an accurateand constant web tension. Selection of the ratio of the rotationalspeeds does not preclude that the rotational speed of the conveyorrollers, taken alone, is too high or too low with reference to therotational speed of the press. Moreover, changes in the rotationalspeed, in particular of the cooling rollers that is, the rollersdisposed posterior of the printing units-do not act back fully upon thefirst printing unit, and accordingly substantial drops of tension mayeasily occur along the length of the web.

THE INVENTION It is the broad object ofthe invention to provide a noveland improved device of the general kind above referred to with which aconstant tension of the web can be continuously and accuratelymaintained.

A more specific object of the invention is to provide a novel andimproved device of the general kind above referred to with which aselected ratio of the rotational speeds is maintained between a firstand a second couple of conveyor rollers, that is, between a coupleanterior and a couple posterior of the printing unit or units of thepress, and with which further the rotational speed of the first oranterior couple is regulated in accordance with a desired tension of theweb portion between said first couple and the printing unit adjacentthereto. The ratio of rotational speeds of said two couples is selectedin accordance with the web material and the printing operations to beeffected.

SUMMARY OF THE INVENTION Basically, the device according to theinvention comprises a first device for measuring and visually indicatingdifferentials between the rotational speeds or the circumferentialspeeds of an anterior and posterior couple of conveyor rollers, saidspeed differentials being preferably indicated by means of digits. Thedigital indications are used to set the speed differential to a selectedor required value by means of finely adjustable variable speed gearingmeans. The device further comprises a speed regulating device disposedposterior of the first or anterior couple but anterior of the firstprinting unit, and automatically regulating the tension of the webportion between said first couple and said first printing unit.Accordingly, the invention in effect resides in the combination andcoaction of two speed controlling means each of which may beconventional as such.

Applicant has found that neither one of the two control means is singlycapable of performing the required tension control, but that thecoaction of the two control means in dependence one on the other resultsin a surprisingly successful and reliable tension control. The automaticspeed control of the first or anterior couple by the second device so asto effect a constant tension of the web portion anterior of the firstprinting unit, has a advantageous effect, not only upon the firstprinting unit but also upon subsequent printing units even though suchfavorable effect gradually decreases. As the speed control of the secondor posterior couple is based upon a comparison of the rotational speedsof the couples, and such comparison is preceded by the speed control ofthe first couple, it is assured that the web tension in the press isaffected at the other end of the press in accordance with the proposedsolution of the problem with which the invention is concerned.

In other words, the concept of the invention resides in combining thecontrol means of the device to a single tightly coacting control system.

The comparison of the rotational or circumferential speeds of thecouples is preferably effected by photoelectric or magnetic pulses andthe indication of the detected speed differential can be obtained byelectronic digital counters count ing the number of pulses and directlyindicating the obtained sum total of the numbers. It has been found thathighly accurate comparison values can be obtained in this manner.

The device for regulating the speed of the first or anterior couple ofconveyor rollers may include a so-called floating roll which detects thetension of the respective web portion and reacts to the detected tensionby correspondingly changing its spatial position. Such changes inposition are utilized to control a suitable instrument which in turncauses the required speed regulation of the first couple. Suchinstrument can be mechanically, electrically, pneumatically or opticallyoperated. If a swinging roller instead of a floating roller is used, asit is also possible, an auxiliary weight may be provided which variesthe tension of the web portion and such auxiliary weight can bepositionally adjusted by a electrically operated remote control device.

The invention also contemplates that the regulating means for finelyadjusting the rotational or circumferential speeds of the rollers of thesecond or posterior couple are remote controlled. The required remotecontrol device is preferably disposed in spatially close relationshipwith the device for indicating the aforedescribed speed differentialbetween the couples. Such an arrangement permits control of the webtension from a central station. By locating the device for indicatingthe speed differentials and the remote control device for varying therelative rotational speed of the couples next to a control board forthe-press itself and also next to the remote control device for theauxiliary weight, the entire operation of the press can be convenientlycontrolled from a central station.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION In the singleFlGURE of the drawing, a deviceaccording to the invention isdiagrammatically shown by way of illustration and not by wayoflirnitation.

Only those components of the press and the device are indicated whichare essential for the understanding of the invention.

Referring now to the FIGURE in detail, there is shown a web I such as apaper web which is withdrawn from a web supply device 2 including a webroll (only diagrammatically shown), and is guided to a first couple 3 oftwo conveyor rollers. The web supply device 2 may include means forexchanging the web roll and also means (not shown) for assuring a smoothand jerk-free withdrawal of the web from the roller.

The web after passing couple 3 is guided over guide rolls 4 to define aloop in which a floating roll 5 is suspended, the function of which willbe more fully described hereinafter.

After leaving guide rolls 4 the web passes successively through printingunits 6 and 7 of the press. Two such units are shown, but it should beunderstood that there may be only one unit or more than two. Similarly,it should be understood that there may be more than one couple 3anterior of the first unit After leaving unit 7 the web is guidedthrough a drying device 8 to a couple 9 of two conveyor rollers whichmay simultaneously constitute cooling rollers. The web may be guidedfrom couple9 to suitable and conventional folding and cutting mechanisms(not shown).

The rollers of both couples are driven by means of a main-- drive motor(not shown) which is coupled to the rollers via speed adjustabletransmission means I0 and M, respectively, such as so-called P.l.V.gearing means with finely variable transmission ratio. The transmissionratios of gcarings I0 and II can be independently controlled bydiagrammatically in-:- dicated setting motors 12 and I3, respectively,such as servo-- motors.

As is now evident, the relative rotational or circumferential.

speeds of the couples 3 and 9 can be adjusted relative to each other.

The aforementioned floating roll 5 constitutes part of a regulatingdevice for automatically maintaining constant the-'- tension of the webportion between couple 3 and printing unit 6. As is evident, the depthof the loop between guide rolls 4' and thus the spatial up and downposition of roll 5 are a function of the tension of the web portion tobe supervised for a given weight of the roll. Conversely, by changingthe weight of the roll, the spatial position thereof is changed for agiven ten-' sion.

The up and down movements of roll 5 as the tension'of the web portionbetween couple 3 and unit 6 changes are utilized to control speedsetting motor 12 for couple 3. As indicated before, there are well knownand readily available many means for translating the up and downmovements of roll 5 into a control of motor 12. There is shown by way ofexample; a potentiometer 15 of conventional design, the contact slider15a of which is carried by roll 5. When the roll is in a positionreflecting the correct tension of the web portion, such as a midposition, the slider is in a neutral position, butit activates motor 12in one'or the other direction as the rolI,-and with it the slider, moveup or down thereby either increasing or decreasing the ratio oftransmission of gearing 10 as required, thus eventually causing returnof'roll 6 into its neutral position.

There is furthershown a control console or panel 16 for the printingpress. A control panel 17 next to console 16 mounts the devices requiredfor supervising and controlling the web tension. There isdiagrammatically shown an instrument 18::

such as a digital counter coupled to devices 19 and 20 which coact withcouples 3 and 9 respectively, to detect the rotational speeds of the,couples and to transmit appropriate signals, for instance voltage ormagnetic pulses. to instrument 18.'Control panel 17 further accommodatesa remote control device 21 of conventional design which is coupled, asit is in-- dicated byarrowed lines, to motors I9 and 20 controlling theratios of transmissions and individually operable by suitable means suchas pushbutton switches '22 and 23, one pushbutton:

being provided for each of the motors I) and 20.

The control panel 17 is also coupled to the automatic speed regulatingdevice including roll 5 and potentiometer 15. As this device bringsthetension of the web portion between couple 3 and printing unit 6 to thedesired value, the speed differential between couples 3 and 9 can bebrought to the selected value by adjusting couple 9 via motor 13 andgearing 11.

I claim:

1. A device for maintaining constant the tension of a web conveyed froma web supply through at least one printing unit of a printing press,said device comprising in combination:

a first couple of power-driven conveyor rollers for conveying said webdisposed anterior of the printing unit; a second couple of power-drivenconveyor rollers for conveying said web disposed posterior of theprinting unit;

transmission means with variable transmission ratio coupled to each ofsaid couples for varying the rotational speed of the rollers of therespective couple;

speed measuring and indicating mean connected to each of the couples,said means measuring and visually indicating speed differentials betweensaid two couples for adjusting the speed differential to a selectedvalue by varying the. transmission ratio of at least one of saidtransmissionmeans; and

automatic speed control means including detecting means detecting thetension of the web portion between the first couple and said printingunit, said control means being controlled by said detecting means andcontrolling the transmission ratio of the transmission means coupled tosaid first couple for correspondingly varying the rotational speed ofthe rollers thereof so as to maintain said web portion at a selectedconstant tension.

2. The device according to claim I wherein each of said transmissionmeans comprises a gear train with finely variable gear ratio.

3. The device according to claim 1 wherein each of said measuring andindicating means comprises a digital indicating means numericallyindicating said speed differentials.

4. The device according to claim 1 wherein said automatic speed controlmeans comprises a floating roll suspended in a loop of said web portionfor up and down movement of the roll in accordance with the tension ofsaid web portion, and electric control means controlling thetransmission ratio of the transmission means coupled to the firstcouple, said electric control means including a potentiometer having acontact slider the position of said slider varying in accordance withvariations in the up and down movements of said floating roll.

5. The device according to claim 1 and comprising remote control meansconnected to the transmission means coupled to the second couple forcontrolling the transmission ratio of said transmission means, saidremote control means being located adjacent to said measuring andindicating means thereby providing a common control station.

1. A device for maintaining constant the tension of a web conveyed froma web supply through at least one printing unit of a printing press,said device comprising in combination: a first couple of power-drivenconveyor rollers for conveying said web disposed anterior of theprinting unit; a second couple of power-driven conveyor rollers forconveying said web disposed posterior of the printing unit; transmissionmeans with variable transmission ratio coupled to each of said couplesfor varying the rotational speed of the rollers of the respectivecouple; speed measuring and indicating mean connected to each of thecouples, said means measuring and visually indicating speeddifferentials between said two couples for adjusting the speeddifferential to a selected value by varying the transmission ratio of atleast one of said transmission means; and automatic speed control meansincluding detecting means detecting the tension of the web portionbetween the first couple and said printing unit, said control meansbeing controlled by said detecting means and controlling thetransmission ratio of the transmission means coupled to said firstcouple for correspondingly varying the rotational speed of the rollersthereof so as to maintain said web portion at a selected constanttension.
 2. The device according to claim 1 wherein each of saidtransmission means comprises a gear train with finely variable gearratio.
 3. The device according to claim 1 wherein each of said measuringand indicating means comprises a digital indicating means numericallyindicating said speed differentials.
 4. The device according to claim 1wherein said automatic speed control means comprises a floating rollsuspended in a loop of said web portion for up and down movement of theroll in accordance with the tension of said web portion, and electriccontrol means controlling the transmission ratio of the transmissionmeans coupled to the first couple, said electric control means includinga potentiometer having a contact slider the position of said slidervarying in accordance with variations in the up and down movements ofsaid floating roll.
 5. The device according to claim 1 and comprisingremote control means connected to the transmission means coupled to thesecond couple for controlling the transmission ratio of saidtransmission means, said remote control means being located adjacent tosaid measuring and indicating means thereby providing a common controlstation.